The present invention relates to a microfocus X-ray tube for inspecting an object.
Microfocus X-ray tubes are known, and are used, for example, for inspecting printed circuit boards in the electronics industry. The known X-ray tubes have a head that during operation of the X-ray tubes faces an object that is to be inspected, with a target being disposed on or in the head and being adapted to be bombarded with high energy accelerated electrons, so that in a manner known per se X-ray radiation is emitted. The thus produced X-ray radiation is used in imaging processes in order, for example, to illustrate components or component arrangements on printed circuit boards, and to optically inspect the printed circuit boards in this manner.
Microfocus X-ray tubes are known, the head of which, which during operation faces the object that is to be inspected, has a diameter of several cm. To achieve a great enlargement, it is necessary to bring the focus, and hence the head of the microfocus X-ray tube close enough to the component that is to be inspected. This is possible only if no raised portions are present on the component that is to be inspected and against which the head bufts prior to reaching the required spacing. The known X-ray tubes are thus predominantly suitable for inspecting flat components, whereas they are suitable to only a limited extent for inspecting components that have raised portions, for example loaded circuit boards.
To avoid this drawback, it is known to form the head of the X-ray tubes by a so-called rod anode that is formed by a cylindrical tube having a diameter of only a few cm to a few mm. In particular if the rod anode that is utilized has a diameter of only a few mm, it is possible with such X-ray tubes to also penetrate into narrow depressions, recesses or hollow spaces of a component that is to be inspected.
However, a drawback of such X-ray tubes is that the rod anodes that are used are not very stable, and are therefore sensitive to mechanical damage. To prevent mechanical damage of the rod anodes due to abutment against the component that is to be inspected, it is necessary to carry out the approach of the rod anode to the component that is to be inspected accompanied by optical observation, which requires a high outlay for apparatus and is hence expensive. Furthermore, an optical control of the approach of the rod anode to the component that is to be inspected requires a lot of time and hence results in high personnel costs.
For this reason, it is desirable in practice to use large diameter rod anodes that are not sensitive to mechanical damage.
However, if the head with its flat side, to achieve an inclined radiation through a component that is to be inspected, cannot be brought to the component parallel to its surface, but rather only at an angle to this surface, the drawback is that the danger exists that due to raised portions that are present on the surface, the head cannot be brought close enough to a location of the component that is to be inspected.
It is therefore an object of the present invention to provide a microfocus X-ray tube with which it is also possible to inspect components that are jagged or full of fissures, and which X-ray tube has a robust construction.